This invention relates to an engine induction system having an injector for injecting fuel to an intake manifold.
There has been generally known an engine induction system having an injector for injecting fuel to an intake manifold in which the fuel from the injector is mixed with the air in the intake manifold and supplied to a combustion chamber. Such engine induction system is disclosed, for example, in Unexamined Japanese Patent Publication No. 61-61010.
In an engine induction system of this kind, there have been considered various modifications in which an arrangement of an injector is changed to improve atomization and distributivity of fuel. For example, Unexamined Japanese Patent Publication No. 59-147866 discloses an engine induction system in which two types of injectors are provided in an intake manifold. One injector is used in any operating condition and the other used only in high load operating condition. These injectors are respectively adapted for injecting fuel in designated operating conditions to further atomization of the fuel. Unexamined Japanese Patent Publication No. 61-186061 discloses an engine induction system provided with a main injector and a starting injector in an intake manifold. Unexamined Japanese Patent Publication No. 63-105275 discloses an engine induction system provided with a first injector for injecting fuel at a latter stage of an intake stroke for stratified charge in a combustion chamber and a second injector for supplementarily injecting fuel. Unexamined Japanese Patent Publication No. 61-241461 discloses an engine induction system in which the fuel injected from an injector is supplied to a plurality of intake runners through a distribution pipe.
However, in the conventional engine induction systems, the distance between an injector and an inlet port located at a downstream end of an intake runner is relatively short in order to improve the responsiveness of fuel supply to the combustion chamber and due to a limitation in layout of the engine. Accordingly, the residual time of fuel in the intake runner is short. Consequently, it has been difficult to sufficiently vaporize or atomize the fuel, and mix the fuel with the air in the intake runner.
In the aforementioned system provided with two types of injectors, one injector is disposed more upstream than the other by some distance. However, the distance between the upstream injector and an inlet port of the combustion chamber is too short to provide an intake runner volume equivalent to the stroke volume of a cylinder to which the intake runner is connected. Accordingly, all the fuel injected from the injector is inducted in the cylinder during one intake stroke. Therefore, it has been difficult to provide such a residual time as to ensure vaporization and atomization of fuel and mixing of fuel and air.
Further, there has been generally known an engine provided, in addition to injectors, with an exhaust gas recirculation (hereinafter referred to as an EGR) means for recirculating exhaust gas to the induction system of the engine to improve the emission and the mileage. Specifically, in light and medium load operating zones, the EGR is effected so that nitrogen oxides (hereinafter referred to as NOx) in the engine is reduced. In addition, the mileage will be also improved due to a reduction in pumping loss since introduction of new air to the induction system is restricted and suction pressure is reduced in the EGR. However, if the vaporization, atomization and mixing with fuel and air is insufficient, particularly with a larger amount of recirculated exhaust gas, the combustibility will be deteriorated, resulting in a higher likelihood of ignition failure. Accordingly, the engine provided with the EGR means has faced a drawback that the amount of recirculating exhaust gas cannot be increased to a larger extent and thus cannot attain a satisfactory combustibility.